The automaker began installing the safety feature, known as brake override, only this January after a widely publicized accident involving a runaway Lexus ES that killed four people near San Diego.

Federal regulators in 2007 asked Toyota Motor Corp. to consider installing software to prevent sudden acceleration in its vehicles after receiving complaints that vehicles could race out of control, company documents show.

Yet the automaker began installing the safety feature, known as brake override, only this January after a widely publicized accident involving a runaway Lexus ES that killed four people near San Diego.

Safety regulators acknowledged late last week that they pressured Toyota anew last fall to consider the override software in the wake of that crash, which set off a chain of events leading the company to issue nearly 10 million recall notices worldwide.

Brake override -- software that automatically drops a vehicle's throttle to idle when both the brake and accelerator pedals are depressed simultaneously -- is designed to stop a car even if its engine is accelerating. Lawmakers and safety experts have questioned whether sudden acceleration is responsible for at least 56 deaths and hundreds of injuries in Toyota and Lexus vehicles over the last decade, and since late January have been scrutinizing the automaker's response to the issue.

E-mails and a company memorandum obtained by Congress show that National Highway Traffic Safety Administration investigators discussed brake override with Toyota officials in August 2007, and that in 2008, a year before the San Diego crash, the automaker ordered an internal feasibility study of the technology.

"These documents raise some questions about whether Toyota was doing enough to deal with" sudden acceleration, said Rep. Bruce Braley (D-Iowa), vice chairman of the House Energy and Commerce Committee's investigations panel. "It's obvious that other manufacturers were doing something. Maybe more than Toyota is doing even now."

Toyota spokeswoman Martha Voss declined to comment. "We do not discuss confidential and proprietary documents regarding internal deliberations," she said in a statement.

The automaker began installing brake override in four recalled models in January. In recent weeks, Toyota said it would extend the feature to three other recalled models and make it standard on all new cars by the end of the year.

In the e-mails, officials in Toyota's Washington office describe being asked by federal regulators about the brake override, as well as modifications to the push-button ignition on some vehicles, as part of an ongoing sudden-acceleration investigation involving two Toyota models.

An Aug. 23, 2007, e-mail from Chris Santucci, manager of technical and regulatory affairs in the Washington office, to a superior and seven other Toyota employees noted that at least two other manufacturers were already using brake override at the time.

Santucci, a former NHTSA investigator who joined Toyota in 2003, wrote that he didn't "believe that these functionalities are things [regulators] want Toyota to implement," adding that "there are no requirements to do so."

The investigation was closed seven weeks later without a defect finding by NHTSA. Toyota officials later trumpeted that they "negotiated" a favorable outcome, saving the company more than $100 million.

A year later, a Toyota memo called for an internal study of brake override technology in response to increasing NHTSA pressure over sudden acceleration, but the company did not move to adopt the feature.

The issue resurfaced after the Aug. 28, 2009, Lexus crash near San Diego. The driver, California Highway Patrol Officer Mark Saylor, was killed along with his wife, daughter and brother-in-law, who made a 911 call before impact.

"I will do everything in my power to assure such a tragedy never happens again," Akio Toyoda, president of Toyota, told Congress last month.

Attorney John Gomez, who is representing Saylor's family in a lawsuit filed against the automaker, contends the crash was avoidable.

"If there was brake override on that vehicle, then for sure those deaths would not have happened," Gomez said. "This is something that was clearly feasible long ago."

Toyota has said that it believes that floor mat entrapment of accelerator pedals and sticking gas pedals are the causes of sudden acceleration in its vehicles, a problem that has bedeviled the company for the last decade. In response to public skepticism about those explanations, both it and NHTSA are reviewing the possibility that the electronic throttle system in its vehicles could cause the problem.

Some lawmakers believe a brake override feature could be the silver bullet, rendering such questions moot. In a hearing this month, Sen. John D. Rockefeller (D-W.Va.) described it as "the solution" and called for legislation mandating it on all vehicles.

Asked about the newly disclosed documents, NHTSA said in a statement that it discussed brake override with Toyota in 2007 as part of an investigation of unintended acceleration in the Camry and Lexus ES, but did not insist on the fail-safe feature.